Pattern forming method, semiconductor device manufacturing method and exposure mask set

ABSTRACT

First, a first exposure process is performed using dipole illumination with only a grating-pattern forming region as a substantial object to be exposed. Next, a second exposure process is performed with only a standard-pattern forming region as a substantial object to be exposed. A development process is then performed to obtain a resist pattern. A mask for the first exposure process is such that a light blocking pattern is formed on the whole surface of a standard-pattern mask part corresponding to the standard-pattern forming region. A mask for the second exposure is such that a light blocking pattern is formed on the whole surface of a grating-pattern mask part corresponding to the grating-pattern forming region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a pattern forming method, and in particular toa resist pattern forming method including both a grating pattern, whichis a fine pattern, and a pattern of arbitrary shape, in a lithographystep in the course of a process of manufacturing a semiconductor device.

2. Description of the Background Art

The shrinking of semiconductor circuit patterns in recent years islargely attributable to the progress of optical lithography technique,which mainly results from wavelength shortening of an exposure lightsource. However, ways of shrinking patterns other than the wavelengthshortening have been studied in many fields due to price increases inexposure device. For example, as a result of the progress such asenlargement of the aperture of a lens by scanner-type exposuretechnique, modified illumination technique, super-resolution masktechnique or the like, there is a growing trend to shrink manufacturingdimensions of a pattern while maintaining an exposure wavelength. Areversed phenomenon has taken place from a 0.18 μm (180 nm) generationon down in which manufacturing dimensions are less than an exposurewavelength (KrF Excimer laser: 248 nm).

In forming a fine pattern less than the wavelength of light that is usedfor exposure, techniques using a half-tone phase shift mask, a phaseshift mask, and a modified illumination technique are well known. Intechniques using the masks, a special mask is used having a portionthereon for inverting the phase of light of an exposure wavelength, forexample, to enhance optical intensity contrast on an image-formingsurface by an optical interference effect.

In the modified illumination technique, a mask surface is illuminated byoptimizing the shape of illumination such that all complicated circuitpatterns designed on the mask are formed with stability in dimensionsand two-dimensional shapes thereof, to enhance optical intensitycontrast of all the patterns on an image-forming surface.

For example, with a fine circuit pattern that includes a pattern(grating pattern (repetition pattern)) in a lattice having fine linesand spaces being repeated alternately, and a pattern (standard pattern)provided to be partly continuous with the grating pattern and to havelarger dimensions than the grating pattern, the shape of illuminationhas been optimized such that excellent optical contrast is obtained forthe fine circuit pattern.

A typical example is the optimization of an outer contour radius (outerdiameter R1) and an inner contour radius (inner diameter R2) of annularillumination that blocks light circularly at the center of anillumination optical system. The sizes of four openings of four-lensillumination have been optimized as well.

U.S. Pat. No. 5,858,580 discloses forming a fine circuit pattern by atwo-exposure process, in which a wiring portion thinner than an exposurewavelength is formed using a phase shift mask and the other portions areformed using a standard mask. This method is being put to practicallyuse.

In addition, U.S. Pat. No. 5,415,835 and Japanese Patent ApplicationLaid-Open No. 2000-349010 disclose forming a fine circuit pattern by amultiple exposure process including a two-exposure process. U.S. Pat.No. 5,415,835 discloses a technique of fabricating a fine pattern byperforming a dual beam interference exposure with a device other thanstandard reduced projection exposure devices. Further, U.S. Pat. No.5,858,580, Japanese Patent Application Laid-Open No. 2000-349010, U.S.Pat. Nos. 6,228,539, 6,258,493 and 6,566,023, and United States PatentApplication Publication No. 2004-197680 disclose a method in which astandard exposure step and a fine isolated wiring pattern (gate pattern)or fine periodic pattern exposure step are performed withoutintervention of a development process, the fine isolated wiring patternor fine periodic pattern exposure step being performed using a Levensontype phase shift mask (Alternative Phase Shift Mask) in whichphase-inverted complete transmissive areas are juxtaposed to each other.Furthermore, International Patent Application Publication No. WO99/65066and Japanese Patent Application Laid-Open No. 2000-021718 disclose amethod of forming a periodic pattern using dipole illumination, andforming an isolated pattern by erasing the periodic pattern other than apartial wiring in the periodic pattern with a standard pattern by meansof exposure.

The following equation (1) is the Rayleigh equation indicative ofoptical resolution:R=k1·(λ/NA)   (1)where R is pattern resolution, λ is an exposure wavelength, NA is a lensnumerical aperture, and k1 is a process factor.

It is now assumed that a resist pattern for a fine circuit pattern thatincludes a grating pattern having a process factor k1 of less than“0.3”, and a standard pattern having an arbitrary pattern such as fineisolated space and a process factor k1 of “0.5” level, is subjected topatterning. It may be required in some instances that a grating patternand standard pattern be connected in such resist pattern.

In the conventional techniques described above, it is difficult toresolve this fine circuit pattern with stability no matter how optimizedthe shape of illumination is. For example, setting the NA to “0.85” withthe ArF wavelength (193 nm), the grating pattern of 65 nm L/S will havea process factor k1 of “0.28”. In this case, it was extremely difficulteven with a phase shift mask technique having a process factor k1 ofless than “0.3” to form the fine circuit pattern with high accuracy thatincludes the fine grating pattern and the arbitrary standard patternhaving a process factor k1 of “0.5” level.

This is because when a phase shift mask suitable for the grating patternis used, a phase mismatch associated with the principle of phase shiftmask occurs inevitably due to the pattern arbitrariness, leaving anunintentional and unnecessary pattern on the standard pattern side.Although a negative type resist is commonly used in order to avoid thisproblem, a resist material having excellent resolution characteristicsfor the ArF wavelength is nonexistent, and if it does exist, then theresolution between the same phases will inevitably be insufficient dueto the circuit structure.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a pattern forming methodcapable of forming a fine circuit pattern including a grating patternhaving a process factor k1 of “0.3” or less and a standard patternhaving a process factor k1 of “0.5” level with high accuracy.

In an aspect of this invention, a pattern forming method on a resistformed on a predetermined substrate, with the resist including adjacentfirst and second regions to be patterned, includes the following stepsof: (a) performing a first exposure process with a first exposure maskusing dipole illumination substantially on the first region of theresist, the first exposure mask having a repetition pattern in which aline and space are repeated alternately; (b) performing a secondexposure process with a second exposure mask substantially on the secondregion of the resist, the second exposure mask having a standard patternthat is a pattern excluding the repetition pattern, the standard patternat least partially including a connection pattern continuous with therepetition pattern; and (c) performing a development process on theresist having being subjected to the steps (a) and (b).

An exposure process can be performed that is suitable for each of thefirst and second regions to be provided with the repetition pattern andstandard pattern. The result is that a resist pattern including therepetition pattern and standard pattern that are formed continuouslywith each other through the connection pattern can be obtained with highaccuracy.

In another aspect of this invention, a semiconductor devicemanufacturing method includes the following steps of: (a) forming aresist on a semiconductor substrate or an object to be patterned insidethe semiconductor substrate; (b) patterning the resist using the patternforming method recited in claim 1; and (c) patterning the object to bepatterned with the resist having been patterned as a mask.

The object to be patterned can be patterned with high accuracy.

In another aspect of this invention, an exposure mask set includes firstand second exposure masks. The first exposure mask includes adjacentfirst and second mask parts, the first mask part having a repetitionpattern in which a line and space are repeated alternately. The secondexposure mask includes first and second mask parts equivalent to thefirst and second mask parts of the first exposure mask, the second maskpart having a standard pattern that is a pattern excluding therepetition pattern, at least part of the standard pattern including aconnection pattern for being continuous with the repetition pattern. Thefirst exposure mask is provided with a light blocking region on thewhole surface of the second mask part, and the second exposure mask isprovided with a light blocking region on at least part of the first maskpart. The first and second exposure masks each include a transmissivepart, a half-tone phase shift mask part transmitting light only at apredetermined ratio and inverting a phase of light being transmittedtherethrough, and a light blocking part having a smaller transmissionfactor than the predetermined ratio. The second mask part of the firstexposure mask is formed at least of the light blocking part in a regionexcluding a boundary adjacent region between the first and second maskparts. The first mask part of the second exposure mask is formed atleast of the light blocking part in a region excluding the boundaryadjacent region.

The second mask part excluding the boundary adjacent region blocks lightduring the first exposure process with the first exposure mask, and thefirst mask part excluding the boundary adjacent region blocks lightduring the second exposure process with the second exposure mask.

The result is that no part of the repetition pattern is subjected tolight transmission during the second exposure process, allowing therepetition pattern to be obtained with high accuracy. In addition, sinceno part of the standard pattern is subjected to light transmissionduring the first exposure process, allowing the standard pattern to beobtained with high accuracy.

These and other objects, features, aspects and advantages of thisinvention will become more apparent from the following detaileddescription of this invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flow chart for a pattern forming method accordingto a first preferred embodiment of this invention;

FIG. 2 illustrates the plane shape of a resist pattern to be finallyobtained;

FIG. 3 depicts the structure of an illumination system stop for dipoleillumination used in a first exposure process;

FIG. 4 explains an optical interference condition in the first exposureprocess;

FIG. 5 illustrates the plane shape of an HT mask used in the firstexposure process;

FIG. 6 depicts the structure of an illumination system stop for ⅔annular illumination used in a second exposure process;

FIG. 7 illustrates the plane shape of an HT mask used in the secondexposure process;

FIG. 8 illustrates a resist pattern formed when a mask for the firstexposure process is overlaid on the mask for the second exposure processwith a deviation in a rightward-slanting rear direction;

FIG. 9 illustrates a resist pattern formed when the mask for the firstexposure process is overlaid on the mask for the second exposure processwith a deviation in a leftward-slanting rear direction;

FIG. 10 illustrates the plane structure of an imaginary resist patternfocusing only on a grating pattern;

FIG. 11 illustrates the plane structure of an assumed resist pattern inview of an edge recession phenomenon shown in FIG. 10;

FIG. 12 illustrates the plane structure of an HT mask used in the secondexposure process according to a second preferred embodiment of thisinvention;

FIGS. 13 to 15 illustrate resist patterns obtained by pattern formingmethods according to the second preferred embodiment;

FIG. 16 illustrates an HT mask for the first exposure process inobtaining the resist pattern shown in FIG. 15;

FIG. 17 depicts an HT mask for the second exposure process in obtainingthe resist pattern shown in FIG. 15;

FIG. 18 illustrates a resist pattern obtained by a pattern formingmethod according to the second preferred embodiment, with the resistpattern shown in FIG. 15 as a desired pattern;

FIGS. 19 and 20 illustrate resist patterns obtained by pattern formingmethods according to the second preferred embodiment;

FIG. 21 illustrates the plane structure of a triton mask used in thefirst exposure process according to a third preferred embodiment of thisinvention;

FIG. 22 illustrates the plane structure of a triton mask used in thesecond exposure process according to the third preferred embodiment;

FIG. 23 illustrates the plane structure of a resist pattern obtained bya pattern forming method according to the third preferred embodiment;

FIG. 24 illustrates a triton mask used in the second exposure process ina second mode according to the third preferred embodiment;

FIG. 25 illustrates a triton mask used in the first exposure process ina third mode according to the third preferred embodiment;

FIG. 26 illustrates an optical simulation result of a connection portionin a resist pattern obtained by a pattern forming method of a first modeaccording to the third preferred embodiment;

FIG. 27 illustrates an optical simulation result of a connection portionin a resist pattern obtained by a pattern forming method of the secondmode according to the third preferred embodiment;

FIG. 28 illustrates an optical simulation result of a connection portionin a resist pattern obtained by a pattern forming method of the thirdmode according to the third preferred embodiment;

FIG. 29 illustrates a triton mask used in the first exposure process ina fourth mode according to the third preferred embodiment;

FIG. 30 illustrates a flow chart for an exposure method to be performedon a plurality of wafers according to a fourth preferred embodiment ofthis invention; and

FIG. 31 depicts the structure of another illumination system stop usedin the second exposure process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Preferred Embodiment

(General Process)

FIG. 1 illustrates a flow chart for a pattern forming method accordingto a first preferred embodiment of this invention. This method willgenerally be described.

First, at step S1, a resist is applied to the surface of a predeterminedsubstrate. The predetermined substrate as used herein means a substratehaving a silicon wafer and a film subject to pattern formation formedthereon such as polysilicon, tungsten, a silicon oxide film, a siliconnitride film or aluminum, or the substrate itself.

The resist application as used herein means, for example, forming anorganic anti-reflection film in a thickness of about 78 nm on thepredetermined substrate, and applying a methacrylic-system chemicallyamplified positive type resist in a thickness of about 180 nm on theorganic anti-reflection film.

FIG. 2 illustrates the plane shape of a resist pattern (desired pattern)to be finally obtained.

As shown, the desired pattern has a plane shape such that agrating-pattern forming region A1 (first region) where a grating pattern100 is formed and a standard-pattern forming region A2 (second region)where a standard pattern 101 is formed are separately formed adjacentlyto each other, while part of the grating pattern 100 and part of thestandard pattern 101 are connected in a connection region A3 adjacent toboth the regions A1 and A2.

In FIG. 2, line patterns 11 to 14 are arranged in a lattice as thegrating pattern 100, and patterns 21 to 24 (21: arbitrary pattern, 22and 24: pad pattern, 23: wiring pattern) are arranged in arbitraryfashion as the standard pattern 101. The line pattern 12 and wiringpattern 23 are connected, and the line pattern 14 and pad pattern 24 areconnected. The “standard pattern” as used in this specification meanspatterns other than the grating pattern.

Subsequently, at step S2, heat treatment before exposure (soft bake) isperformed for about 60 seconds at a temperature of about 110° C., forexample.

Next, at step S3, a first exposure process is performed with only thegrating-pattern forming region A1 as a substantial object to be exposed.The ArF Excimer laser (wavelength: 193 nm) is used as an exposure lightsource in this process. This process will be described later in detail.

Next, at step S4, a second exposure process is performed with only thestandard-pattern forming region A2 as a substantial object to beexposed. The ArF Excimer laser (wavelength: 193 nm) is used as anexposure light source in this process. This process will be describedlater in detail.

Then, at step S5, heat treatment after exposure (PEB: Post ExposureBake) is performed for about 60 seconds at a temperature of about 125°C., for example.

Thereafter, at step S6, a development process is performed to subjectthe resist to patterning. A 2.38 wt % aqueous solution of tetramethylammonium hydroxide may be used as a developer in this process. Theresult is that the resist is patterned into the desired patternmentioned above. The development process is followed by heat treatmentfor dehydration for about 60 seconds at a temperature of about 115° C.,for example.

(First Exposure Process)

In the first exposure process, the ArF Excimer laser (wavelength: 193nm) is used as radiation, for example, and dipole illumination is usedas illuminating means.

FIG. 3 depicts the structure of an illumination system stop for dipoleillumination used in the first exposure process. The use of dipoleillumination with an illumination system stop 31, which is provided withtwo openings 32, allows for dual beam interference exposure byzero-order diffraction light and first-order diffraction light. The twoopenings 32 are arranged in a direction in which the lines and spaces ofthe grating pattern are repeated. That is, when the lines and spaces ofthe grating pattern 100 are repeated longitudinally (horizontal-stripedpattern) as shown in FIG. 2, the openings 32 are arranged at the top andthe bottom as shown in FIG. 3.

FIG. 4 explains an optical interference condition in the first exposureprocess. How (λ/P) is obtained will be explained with reference to thisdrawing. In FIG. 4, exposure light 36 enters an HT (half-tone phaseshift) mask 35 to be diffracted, the HT mask 35 having a light blockingpattern 34 that form the grating pattern 100 being formed on a glasssubstrate 33. The exposure light 36 having been diffracted is indicatedas exposure light 37.

In this case, an optical path difference A between the exposure lights36 and 37 is expressed by the following equation (2):Δ=d1+d2=P (sinθi+sinθd)=λ  (2)where P is a pitch of the grating pattern, θi is an incident angle, θdis a diffraction angle, and as mentioned above, λ is an exposurewavelength. The equation (2) tells that an ideal optical interferencecondition will be attained when (λ+P)=sinθi+sinθd.

Here, on conditions of λ=193 nm, NA=0.85, P=130 nm (grating pattern inwhich spaces and lines are arranged with 65 nm-pitches), and iNA=0.81,inner sigma σin and outer sigma σout are obtained by applying (λ+P)obtained from the above equation (2) to the following equations (3) and(4). The iNA is an illumination numerical aperture of an exposuredevice, and NA is a numerical aperture of a projection lens.σin={(λ/P)−NA}/NA   (3)σout=iNA/NA   (4)

The result is that the inner sigma σin and outer sigma σout of theopenings 32 shown in FIG. 3 are obtained as “0.75” and “0.95”,respectively.

An increase in cutting angle of circular arcs of the openings 32 of theillumination system stop 31 for dipole illumination shown in FIG. 3 willresult in deterioration of contrast, but enhancement of illumination.Accordingly, an optimum value for the cutting angle is selected based ona trade-off between them.

In addition, it will be appreciated that the openings 32 could haveother shapes than that in FIG. 3 as long as they satisfy the aboveoptical interference condition.

FIG. 5 illustrates the plane shape of an HT mask used in the firstexposure process. As shown, an HT mask 1 for the first exposure is suchthat a light blocking pattern 41 and transmissive pattern 42 are formedalternately on a grating-pattern mask part M1 (first mask part)corresponding to the grating-pattern forming region A1, and a lightblocking pattern 43 is formed on the whole surface of a standard-patternmask part M2 (second mask part) corresponding to the standard-patternforming region A2. The light blocking pattern 41 is provided to form theline patterns 11 to 14 shown in FIG. 2. The light blocking patterns 41and 43 of the HT mask 1 have a transmission factor of 6%.

An HT (half-tone phase shift) mask is described. An HT mask includes atransmissive part (which corresponds to the transmissive pattern 42)transmitting high intensity light that contributes to exposure, and alight blocking part (which corresponds to the light blocking pattern 41)having a transmission factor of about 6% and inverting the phase oflight being transmitted. The adoption of an exposure technique with suchHT mask allows for contrast enhancement on an image-forming surface.

With the dipole illumination using the HT mask 1, the first exposureprocess is performed with only the grating-pattern forming region A1 asa substantial object to be exposed.

(Second Exposure Process)

FIG. 6 depicts the structure of an illumination system stop for ⅔annular illumination used in the second exposure process. As shown, anillumination system stop 38 includes an annular opening 39, with theratio between an inner diameter R1 from the center to the opening 39 andan outer diameter R2 from the center to the opening 39 being set to 2:3.The use of the illumination system stop 38 thus allows for ⅔ annularillumination. The numerical aperture NA is set to “0.85”. Exposureconditions in the second exposure process including the amount ofirradiation and a focus position are respectively optimized.

FIG. 7 illustrates the plane shape of an HT mask used in the secondexposure process. As shown, an HT mask 2 for the second exposure is suchthat a light blocking pattern 55 is formed on the whole surface of thegrating-pattern mask part M1, and light blocking patterns 51 to 54 areformed on the standard-pattern mask part M2. In the standard-patternmask part M2, a region where the light blocking patterns 51 to 54 arenot formed is a transmissive region. The light blocking patterns 51 to54 are provided to form the patterns 21 to 24 of the standard pattern101 shown in FIG. 2.

With the ⅔ annular illumination using the HT mask 2, the second exposureprocess is performed with only the standard-pattern forming region A2 asa substantial object to be exposed.

Therefore, in the first preferred embodiment, an exposure mask setincluding the HT mask 1 for the first exposure and HT mask 2 for thesecond exposure is used so that a pattern including the grating pattern100 and standard pattern 101 can be formed on the resist with highaccuracy.

(Effect)

As has been described, the desired pattern shown in FIG. 2 is obtainedby the pattern forming method according to the first preferredembodiment. Observation by an electron microscope of the resist patternobtained by this pattern forming method confirmed that a patternincluding a grating pattern of 65 nm L/S and a peripheral circuitpattern which is a standard pattern that are formed continuously witheach other, just like the desired pattern shown in FIG. 2, had beenresolved.

As described above, in the pattern forming method according to the firstpreferred embodiment, the first exposure process for forming the gratingpattern is performed with only the grating-pattern forming region A1 asa substantial object to be exposed, by using dipole illuminationsuitable for exposure of a fine pattern (having a process factor k1 of0.3 or less, for example). In addition, the second exposure process forforming the standard pattern is performed with only the standard-patternforming region A2 as a substantial object to be exposed, by usingisotropic illumination such as annular illumination suitable forexposure of a standard pattern. Namely, the two-exposure processconstitutes an optimum exposure process to obtain the desired patternshown in FIG. 2.

Accordingly, a resist pattern for a circuit pattern that includes both agrating pattern having a process factor k1 of less than “0.3”, and astandard pattern having a process factor k1 of 0.5 level can be obtainedwith high accuracy.

The formation with high accuracy of a circuit pattern in which a gratingpattern and standard pattern are formed separately while beingcontinuous with each other allows for the designs of circuit patternshaving various kinds of shapes.

In addition, in the pattern forming method according to the firstpreferred embodiment, the light blocking pattern 43 is provided on thewhole surface of the standard-pattern mask part M2 during the firstexposure process, and the light blocking pattern 55 is provided on thewhole surface of the grating-pattern mask part M1 during the secondexposure process, so that exposure can be performed only on thegrating-pattern forming region A1 in the first exposure process and onlyon the standard-pattern forming region A2 in the second exposureprocess. This attains optimum exposure for each of the grating pattern100 and standard pattern 101 formed on the grating-pattern formingregion A1 and standard-pattern forming region A2, respectively.

The pattern forming method according to the first preferred embodimentis also a cost-effective method, because it is performed using theexisting exposure devices and the like, so no new exposure devices andthe like need to be additionally introduced when performing the firstand second exposure processes.

The sequence of the first and second exposure processes may be reversed.Namely, the first exposure process may be performed after the secondexposure process.

Further, although the resist is exposed to the standard pattern by asingle exposure step in the second exposure process according to thefirst preferred embodiment, the resist may be exposed to the standardpattern by two or more partial exposure steps in the second exposureprocess. The number of partial exposure steps will be selected inarbitrary fashion depending on the shape of standard pattern, forexample.

When performing a plurality of partial exposure steps in the secondexposure process, the amount of irradiation and an exposure focusposition may naturally be optimized in each partial exposure step. Suchoptimizations may be performed in the first exposure process as well, asmentioned above.

Thus, appropriate exposure conditions may be set for each pattern to beformed in each partial exposure step in the second exposure process thatincludes the plurality of partial exposure steps. This allows forresolution enhancement of the whole pattern in order to obtain a desiredpattern such as is shown in FIG. 2.

(Modification)

The pattern forming method according to the first preferred embodimentconcerns a pattern including a grating pattern in which lines and spacesare repeated only in one direction and a standard pattern. As amodification, exposures are performed based on the assumption that agrating pattern (lines and spaces) is repeated in two directions (firstand second directions orthogonal to each other), namely, a gratingpattern includes a first partial grating pattern in which lines andspaces are repeated alternately in the above first direction and asecond partial grating pattern separately formed in which lines andspaces are repeated alternately in the above second direction.

In this case, it is effective to change a illumination condition ofdipole illumination when forming the first and second partial gratingpatterns by rotating the stops of dipole illumination shown in FIG. 3 by90 degrees. That is, the patterns will be formed on the resist by thefollowing steps:

First, as a first step of the first exposure process for gratingpattern, an exposure process is performed under a first illuminationcondition with the dipole illumination stops in which the two openings32 are arranged in the above first direction, using a first partialgrating pattern mask having the first partial grating pattern.

Next, as a second step of the first exposure process for gratingpattern, an exposure process is performed under a second illuminationcondition with the dipole illumination stops in which the two openings32 are arranged in the above second direction, using a second partialgrating pattern mask having the second partial grating pattern.

Then, as a step of the second exposure process, an exposure process isperformed under a third illumination condition with isotropicillumination such as annular illumination, using an exposure mask havingthe standard pattern that includes a connection portion to the gratingpattern.

Lastly, the resist is subjected to development.

In this manner, the first and second partial grating patterns aresubjected to exposure under different illumination conditions havingdifferent contents of the dipole illumination stops, thus setting anoptimum illumination condition for each of the first and second exposureprocesses. Accordingly, a fine pattern that includes a grating pattern(first and second partial grating patterns) having a process factor k1of 0.3 or less both longitudinally and horizontally can be formed withhigh accuracy.

Second Preferred Embodiment

(Premise)

The finally obtained grating pattern by the pattern forming methodaccording to the first preferred embodiment is thinner than a resistpattern immediately after the first exposure process, and verticallydeteriorated in resist shape. This is possibly the consequence of beingsubjected to half-tone transmitted light (light being transmittedthrough the light blocking pattern 55) during the second exposureprocess. As a result, the contrast in a composite optical image of themask for the first exposure and mask for the second exposuredeteriorates, further causing deterioration in line edge roughness(straightness of wiring). Improvements are made to these deteriorationsin a second preferred embodiment of this invention.

(General Process)

A general process is performed in the same fashion as the firstpreferred embodiment illustrated in FIG. 1, except the contents of thesecond exposure process at step S4.

(Study of Various Problems)

FIG. 8 illustrates a resist pattern formed when the mask for the firstexposure process is overlaid on the mask for the second exposure processwith a deviation in a rightward-slanting rear direction. Formed as aresult between the grating pattern 100 and standard pattern 101 is anunnecessary pattern 10 that connects the line patterns 11 to 14 and thewiring patterns 23 and 24. A short circuit will disadvantageously occurbetween the line pattern 11 and the line pattern 12 (wiring pattern 23)when set to different potentials.

FIG. 9 illustrates a resist pattern formed when the mask for the firstexposure process is overlaid on the mask for the second exposure processwith a deviation in a leftward-slanting rear direction. As a result, theline pattern 13 and pad pattern 24 get unnecessarily connected.

FIG. 10 depicts the plane structure of an imaginary resist patternfocusing only on a grating pattern. An imaginary resist pattern 25 asshown is assumed to be obtained after being subjected to the firstexposure process using the HT mask 1 shown in FIG. 5, and then adevelopment process. In the imaginary resist pattern 25, as shown inFIG. 10, grating pattern edges corresponding to the transmissivepatterns 42 shown in FIG. 5 recede (an edge recession phenomenon occurs)from the mask dimensions on the optical principle caused by the shape ofpattern, leaving recession residual patterns 26.

FIG. 11 depicts the plane structure of an assumed resist pattern in viewof the edge recession phenomenon shown in FIG. 10. As shown, therecession residual patterns 26 connects the line patterns 11 and 12, 12and 13, and 13 and 14, to form an unnecessary electric connectionpattern 27 on each side of the line patterns 11 to 13. The unnecessaryelectric connection pattern 27 is disadvantageously further connected tothe wiring pattern 23 and pad pattern 24. As such, problems arise notonly by the deviations of masks as shown in FIGS. 8 and 9, but also bythe edge recession phenomenon shown in FIG. 10.

(Second Exposure Process)

In view of the various problems mentioned above, improvements are madeto the HT mask used in the second exposure process according to thesecond preferred embodiment.

FIG. 12 illustrates the plane structure of an HT mask used in the secondexposure process according to the second preferred embodiment.

As shown, an HT mask 4 for the second exposure is such that a reducedlight blocking pattern 56 that is reduced by a predetermined amount Cfrom each side of the light blocking pattern 55 of the HT mask 2 shownin FIG. 7 is formed on the grating-pattern mask part M1. That is, thereduced light blocking pattern 56 is formed on the grating-pattern maskpart M1 except an extension region El (first extension region) extendingfrom a boundary line LB2 between the grating-pattern mask part M1 andthe standard-pattern mask part M2 toward the grating-pattern mask partM1 side by the predetermined amount C (first predetermined amount), andan extension region E2 (second extension region) extending inwardly froman edge line LB5 by the predetermined amount C (second predeterminedamount).

The extension region E2 is thus a transmissive region. Imaginary linepatterns 11 v to 14 v are indicated by dashed lines in order to clarifythe size of the reduced light blocking pattern 56. The edge line LB5corresponds to edge positions of the imaginary line patterns 11 v to 14v.

Meanwhile, a light blocking pattern 53 of the HT mask 4 includes thelight blocking pattern 53 of the HT mask 2 shown in FIG. 7, andadditionally a light blocking pattern extension part 53 c extendingtoward the (inside of) grating-pattern mask part M1 side in theextension region E1, while a light blocking pattern 54 includes thelight blocking pattern 54 of the HT mask 2 shown in FIG. 7, andadditionally a light blocking pattern extension part 54 c extendingtoward the grating-pattern mask part M1 side in the extension region E1.That is, the extension parts 53 c and 54 c of the light blockingpatterns 53 and 54 serving as connection patterns of the standardpattern 101 are provided in the extension region E1.

As such, in the HT mask 4 used in the second exposure process accordingto the second preferred embodiment, the light blocking pattern 53includes a light blocking pattern main part 53 m (which corresponds tothe light blocking pattern 53 of the HT mask 2) and the light blockingpattern extension part 53 c that are formed continuously with eachother, while the light blocking pattern 54 includes a light blockingpattern main part 54 m (which corresponds to the light blocking pattern54 of the HT mask 2) and the light blocking pattern extension part 54 cthat are formed continuously with each other.

The predetermined amount C is determined based on the amount ofrecession due to the edge recession phenomenon, and a tolerance of theoverlay deviation (simple sum of the amount of recession and thetolerance of the overlay deviation, for example).

A wiring width LW of the light blocking pattern extension parts 53 c and54 c is determined as follows: when a line dimension of the gratingpattern is set to 65 nm, for example, a simple sum of a overlaytolerance of 15 nm (vertical and horizontal directions in the planestructure shown in FIG. 12) and a dimensional accuracy tolerance of 10nm (tolerance of finished dimensional deviation) leads to the wiringwidth LW of 115 nm. The tolerances may be obtained by a simple sum or bya root sum square. The dimensions of wiring with a thickness toleranceas defined herein should not be regarded as design dimensions of a mask,but may be regarded as the dimensions of a resist pattern obtained afterexposure and development.

As described above, in the pattern forming method according to thesecond preferred embodiment, the second exposure process is performedusing the HT mask 4 instead of the HT mask 2 of the first preferredembodiment.

(Effect)

FIG. 13 illustrates a resist pattern obtained by the pattern formingmethod according to the second preferred embodiment, where the edgerecession phenomenon occurs with an amount of recession dc1 (<C).

As described above, the HT mask 4 includes the reduced light blockingpattern 56 reduced by the predetermined amount C, and the light blockingpattern extension parts 53 c and 54 c extending by the predeterminedamount C, from the boundary line LB2 toward the grating-pattern maskpart M1 side. Accordingly, the unnecessary electric connection patterns27 (see FIG. 11) not located under the light blocking pattern extensionparts 53 c and 54 c are completely erased during the second exposureprocess.

The result is that wiring pattern extension parts 23 c and 24 c areformed extending from a boundary line LB1 between the grating-patternforming region A1 and the standard-pattern forming region A2 toward thegrating-pattern forming region A1 side only by the amount of recessiondc1, as shown in FIG. 13. The wiring pattern extension part 23 cconnects the wiring pattern 23 and line pattern 12, and the wiringpattern extension part 24 c connects the pad pattern 24 and line pattern14. Therefore, a pattern equivalent to the FIG. 2 pattern in terms ofelectrical connection relationship is obtained even in the event of theedge recession phenomenon.

FIG. 14 illustrates a resist pattern obtained by the pattern formingmethod according to the second preferred embodiment, where the maskoverlay deviation phenomenon in a rightward-slanting direction occurswith an amount of deviation dc2 (<C) to the right (direction in whichthe line pattern 11 is formed (first direction)).

As described above, the HT mask 4 includes the reduced light blockingpattern 56, and the light blocking pattern extension parts 53 c and 54c. Accordingly, the unnecessary pattern 10 (see FIG. 8) not locatedunder the light blocking pattern extension parts 53 c and 54 c iscompletely erased during the second exposure process.

The result is that wiring pattern extension parts 23 c and 24 c areformed extending from the boundary line LB1 toward the grating-patternforming region A1 side only by the amount of deviation dc2, as shown inFIG. 14. The wiring pattern extension part 23 c connects the wiringpattern 23 and line pattern 12, and the wiring pattern extension part 24c connects the pad pattern 24 and line pattern 14. Therefore, a patternequivalent to the FIG. 2 pattern in terms of electrical connectionrelationship is obtained even in the event of the mask overlay deviationphenomenon in a rightward-slanting direction.

Moreover, because the wiring width LW of the light blocking patternextension parts 53 c and 54 c is set wider than the forming width of theline patterns 11 to 14 in view of the overlay tolerance and dimensionalaccuracy tolerance, the line pattern 12 and wiring pattern extensionpart 23 c, and the line pattern 14 and wiring pattern extension part 24c can respectively be connected with reliability even in the event of aoverlay deviation in a vertical direction (second direction).

In this manner, in the pattern forming method according to the secondpreferred embodiment, the second exposure process is performed using theHT mask 4 shown in FIG. 12, thus forming a resist pattern free fromproblems even in the event of the edge recession phenomenon, maskoverlay deviation phenomenon, and so on.

FIG. 15 illustrates a resist pattern formed by the pattern formingmethod according to the second preferred embodiment. As shown, a gratingpattern 102 including line patterns 61 to 69 and a standard pattern 103including patterns 71 to 75 are formed adjacently to each other as adesired pattern. The wiring pattern 71 and line pattern 63, the wiringpattern 73 and line pattern 66, and the wiring pattern 75 and linepattern 68, are respectively continuous with each other.

FIG. 16 illustrates an HT mask for the first exposure process inobtaining a resist pattern 60 shown in FIG. 15. As shown, an HT mask 3for the first exposure is such that a light blocking pattern 44 andtransmissive pattern 45 are formed alternately on the grating-patternmask part M1, and a light blocking pattern 46 is formed on the wholesurface of the standard-pattern mask part M2.

FIG. 17 illustrates an HT mask for the second exposure process inobtaining the resist pattern 60 shown in FIG. 15. As shown, in an HTmask 6 for the second exposure, a reduced light blocking pattern 86reduced by the predetermined amount C from each side of thegrating-pattern mask part M1 is formed on the grating-pattern mask partM1, and light blocking patterns 81 to 85 are formed on thestandard-pattern mask part M2.

The light blocking patterns 81, 83 and 85 additionally include lightblocking pattern extension parts 81 c, 83 c and 85 c, respectively,extending from the boundary line LB2 between the grating-pattern maskpart M1 and the standard-pattern mask part M2 toward the grating-patternmask part M1 side by the predetermined amount C. As described above, thewiring width LW of the light blocking pattern extension parts 81 c, 83 cand 85 c is set in view of the overlay tolerance and dimensionalaccuracy tolerance.

FIG. 18 illustrates a resist pattern obtained by the pattern formingmethod according to the second preferred embodiment, with the resistpattern 60 shown in FIG. 15 as a desired pattern. In FIG. 18, the edgerecession phenomenon occurs with the amount of recession dc1 (<C).

As described above, the HT mask 6 includes the reduced light blockingpattern 86 reduced by the predetermined amount C, and the light blockingpattern extension parts 81 c, 83 c and 85 c extending by thepredetermined amount C, from the boundary line LB2 toward thegrating-pattern mask part M1 side. Accordingly, unnecessary electricconnection patterns (such as the unnecessary electric connectionpatterns 27 shown in FIG. 11 that are caused by the edge recessionphenomenon) not located under the light blocking pattern extension parts81 c, 83 c and 85 c are completely erased during the second exposureprocess.

The result is that wiring pattern extension parts 71 c, 73 c and 75 care formed extending from the boundary line LB1 between thegrating-pattern forming region A1 and the standard-pattern formingregion A2 toward the grating-pattern forming region A1 side only by theamount of recession dc1, as shown in FIG. 18. The wiring patternextension part 71 c connects the wiring pattern 71 and line pattern 63,the wiring pattern extension part 73 c connects the wiring pattern 73and line pattern 66, and the wiring pattern extension part 75 c connectsthe wiring pattern 75 and line pattern 68. Therefore, a patternequivalent to the resist pattern 60 in FIG. 15 in terms of electricalconnection relationship is obtained even in the event of the edgerecession phenomenon.

FIG. 19 illustrates a resist pattern obtained by the pattern formingmethod according to the second preferred embodiment, where the maskoverlay deviation phenomenon in a rightward-slanting direction occurswith the amount of deviation dc2 to the right.

As described above, the HT mask 6 includes the reduced light blockingpattern 86, and the light blocking pattern extension parts 81 c, 83 cand 85 c. Accordingly, unnecessary patterns (which correspond to theunnecessary pattern 10 in FIG. 8) not located under the light blockingpattern extension parts 81 c, 83 c and 85 c are completely erased duringthe second exposure process.

The result is that the wiring pattern extension parts 71 c, 73 c and 75c are formed extending from the boundary line LB1 toward thegrating-pattern forming region A1 side only by the amount of deviationdc2, as shown in FIG. 19. The wiring pattern extension part 71 cconnects the wiring pattern 71 and line pattern 63, the wiring patternextension part 73 c connects the wiring pattern 73 and line pattern 66,and the wiring pattern extension part 75 c connects the wiring pattern75 and line pattern 68. Therefore, a pattern equivalent to the resistpattern 60 shown in FIG. 15 in terms of electrical connectionrelationship is obtained even in the event of the mask overlay deviationphenomenon in a rightward-slanting direction.

Moreover, because the wiring width LW of the light blocking patternextension parts 81 c, 83 c and 85 c is set wider than the forming widthof the line patterns 61 to 69 in view of the overlay tolerance anddimensional accuracy tolerance, the line pattern 63 and wiring patternextension part 71 c, the line pattern 66 and wiring pattern extensionpart 73 c, and the line pattern 68 and wiring pattern extension part 75c can respectively be connected with reliability even in the event of aoverlay deviation in a vertical direction.

FIG. 20 illustrates a resist pattern obtained by the pattern formingmethod according to the second preferred embodiment, where the maskoverlay deviation phenomenon in a leftward-slanting direction occurswith an amount of deviation dc3 to the left.

As described above, the HT mask 6 includes the reduced light blockingpattern 86, and the light blocking pattern extension parts 81 c, 83 cand 85 c. Accordingly, unnecessary patterns (additionally extendingparts of the line patterns 61, 62, 64, 65, 67 and 69 to the boundaryline LB1) not located under the light blocking pattern extension parts81 c, 83 c and 85 c are completely erased during the second exposureprocess.

Moreover, because the wiring width LW of the light blocking patternextension parts 81 c, 83 c and 85 c is set wider than the forming widthof the line patterns 61 to 69 in view of the overlay tolerance anddimensional accuracy tolerance, the line pattern 63 and wiring pattern71, the line pattern 66 and wiring pattern 73, and the line pattern 68and wiring pattern 75 can respectively be connected with reliabilityeven in the event of a overlay deviation in a vertical direction.

Therefore, in the second preferred embodiment, an exposure mask setincluding the HT masks 1 and 3 for the first exposure and HT masks 4 and6 for the second exposure is used so that a pattern including a gratingpattern and standard pattern can be formed on the resist with highaccuracy.

Third Preferred Embodiment

(Premise)

Like the first preferred embodiment, the finally obtained gratingpattern by the pattern forming method according to the second preferredembodiment is thinner than a resist pattern immediately after the firstexposure process, and vertically deteriorated in resist shape. This ispossibly the consequence of being subjected to half-tone transmittedlight through the second HT mask 6 used in the second exposure process.As a result, the contrast of a composite optical image of the first mask(during the first exposure process) and the second mask (during thesecond exposure process) deteriorates, further causing deterioration inline edge roughness (straightness of wiring). Improvements are made tothese deteriorations in a third preferred embodiment of this invention.

(General Process)

A general process is performed in the same fashion as the firstpreferred embodiment illustrated in FIG. 1, except the contents of thefirst exposure process at step S3 and the second exposure process atstep S4.

FIG. 21 illustrates the plane structure of a triton mask 15 used in thefirst exposure process according to the third preferred embodiment.

As shown, the triton mask 15 for the first exposure process is the samein pattern shape itself as the HT mask 1 shown in FIG. 5 for the firstexposure process according to the first and second preferredembodiments. That is, a light blocking pattern 41, transmissive pattern-42 and a light blocking pattern 43 of the triton mask 15 have the sameshapes as the corresponding patterns of the HT mask 1.

The triton mask 15, however, differs from the HT mask 1 in including anHT mask part 15 a, which is an incomplete light blocking part, and acomplete light blocking part 15 b.

The HT mask part 15 a is formed as a region where the whole lightblocking pattern 41 is formed, and extends from a boundary line LB3between the light blocking patterns 43 and 41 by a shift amount ΔD1 tobe formed as part of the light blocking pattern 43 as well.

Meanwhile, the complete light blocking part 15 b is formed as a regionwhere the whole light blocking pattern 43 except the portion of the HTmask part 15 a is formed. That is, the complete light blocking part 15 bis formed on the whole standard-pattern mask part M2 except an adjacentregion (boundary adjacent region) to the boundary line LB2 between thegrating-pattern mask part M1 and standard-pattern mask part M2.

Like the HT mask 1, the HT mask part 15 a includes a transmissive part(which corresponds to the transmissive pattern 42) transmitting highintensity light that contributes to exposure, and a light blocking part(which corresponds to the light blocking pattern 41) having atransmission factor of about 6% and inverting the phase of light beingtransmitted. The complete light blocking part 15 b is a mask part thatblocks light completely by covering a light blocking part equivalent toan HT mask further with Cr or the like.

(Second Exposure Process)

FIG. 22 illustrates the plane structure of a triton mask 16 used in thesecond exposure process according to the third preferred embodiment.

As shown, the triton mask 16 for the second exposure process is the samein pattern shape itself as the HT mask 4 shown in FIG. 12 for the secondexposure process according to the second preferred embodiment. That is,light blocking patterns 51 to 54 and 56 of the triton mask 16 have thesame shapes as the corresponding patterns of the HT mask 4.

The triton mask 16, however, differs from the HT mask 4 in including anHT mask part 16 a, which is an incomplete light blocking part, and acomplete light blocking part 16 b.

The HT mask part 16 a is formed as a region where the whole lightblocking patterns 51 to 54 are formed, and extends from a boundary lineLB4 between the reduced light blocking pattern 56 and the light blockingpattern extension parts 53 c, 54 c by a shift amount ΔD2 to be formed aspart of the reduced light blocking pattern 56 as well.

Meanwhile, the complete light blocking part 16b is formed as a regionwhere the whole reduced light blocking pattern 56 except the portion ofthe HT mask part 16 a is formed. That is, the complete light blockingpart 16 b is formed on the whole grating-pattern mask part M1 except anadjacent region to the boundary line LB2.

(Effect)

FIG. 23 illustrates the plane structure of a resist pattern obtained bythe pattern forming method according to the third preferred embodiment,schematically depicting observed results by an electron microscope.

As shown, it has been confirmed that the grating pattern 100 of 65 nmL/S and standard pattern 101 were subjected to patterning with highaccuracy, and the line pattern 12 and wiring pattern 23, and the linepattern 14 and pad pattern 24 were respectively connected excellently.It was therefore shown that the resist pattern obtained by the patternforming method according to the third preferred embodiment has anexcellent pattern shape without becoming thinner in dimension, ordeteriorated in shape or in straightness like the resist patternsobtained by the methods according to the first and second preferredembodiments.

The effects of the third preferred embodiment are described withreference to FIG. 23. A region EX1 (region on the right side of theboundary line LB4 by the shift amount ΔD2 or more in FIG. 23) equivalentto the most part of the line patterns 11 to 14 is subjected to the firstexposure process with the HT mask part 15 a, and the second exposureprocess with the complete light blocking part 16 b. Accordingly, no partof the region EX1 is subjected to light transmission during the secondexposure process. This prevents the line patterns 11 to 14 in the regionEX1 from being subjected to half-tone transmitted light, and allows theline patterns 11 to 14 to be obtained with high accuracy.

A region EX2 (region on the left side of the boundary line LB3 by theshift amount ΔD1 or more in FIG. 23) equivalent to the most part of thepatterns 21 to 24 is subjected to the first exposure process with thecomplete light blocking part 15 b, and the second exposure process withthe HT mask part 16 a. Accordingly, no part of the region EX2 issubjected to light transmission during the first exposure process. Thisprevents the patterns 21 to 24 in the region EX2 from being subjected tohalf-tone transmitted light, and allows the patterns 21 to 24 to beobtained with high accuracy.

A region EX3 equivalent to a connection region between the gratingpattern 100 in the region EX1 and the standard pattern 101 in the regionEX2 is subjected to the first exposure process with the HT mask part 15a, and the second exposure process with the HT mask part 16 a.Accordingly, the region EX3 is subjected to two light transmissionsthrough the light blocking parts. The effects of the region EX3 will bedescribed later.

(First Mode)

The first and second exposure processes may be performed in other waysthan those described above. A first mode is the pattern forming methoddescribed above that includes the first exposure process with the tritonmask 15 shown in FIG. 21 and the second exposure process with the tritonmask 16 shown in FIG. 22.

(Second Mode)

In a second mode, the first exposure process is performed with thetriton mask 15 shown in FIG. 21, in the same fashion as the first mode.

FIG. 24 illustrates a triton mask used in the second exposure process inthe second mode according to the third preferred embodiment. As shown, atriton mask 18 for the second exposure process is the same in patternshape itself as the HT mask 4 shown in FIG. 12 for the second exposureprocess according to the second preferred embodiment, like the firstmode.

The triton mask 18, however, differs from the HT mask 4 in including anHT mask part 18 a, which is an incomplete light blocking part, and acomplete light blocking part 18 b.

The complete light blocking part 18 b is formed as a region where thewhole reduced light blocking pattern 56 is formed, and extends from theboundary line LB4 between the reduced light blocking pattern 56 and thelight blocking pattern extension parts 53 c, 54 c by a shift amount ΔD4to be formed as parts of the light blocking patterns 53 and 54 as well.That is, the complete light blocking part 18 b is formed as a lightblocking pattern of the whole grating-pattern mask part M1 and anadjacent region to the boundary line LB2.

Meanwhile, the HT mask part 18 a is formed as a region where the entirelight blocking patterns 51 to 54 except the portion of the completelight blocking part 18 b is formed.

The result is that the region EX3 shown in FIG. 23 is subjected to thefirst exposure process with the HT mask part 15 a, and the secondexposure process with the complete light blocking part 18 b.Accordingly, like the region EX1, no part of the region EX3 is subjectedto light transmission during the second exposure process. It is desiredthat the shift amount ΔD4 should be set a little wider than (the shiftamount ΔD1+the predetermined amount C) in order to prevent two lighttransmissions through the region EX3 with reliability.

(Third Mode)

FIG. 25 illustrates a triton mask used in the first exposure process ina third mode according to the third preferred embodiment. As shown, atriton mask 17 for the first exposure process is the same in patternshape itself as the HT mask 1 shown in FIG. 5 for the first exposureprocess according to the first and second preferred embodiments, in thesame fashion as the first and second modes.

The triton mask 17, however, differs from the HT mask 1 in including anHT mask part 17 a, which is an incomplete light blocking part, and acomplete light blocking part 17 b.

The complete light blocking part 17 b is formed as a region where thewhole light blocking pattern 43 is formed, and extends from the boundaryline LB3 between the light blocking patterns 41 and 43 by a shift amountΔD3 to be formed as part of the light blocking pattern 41 as well. Thatis, the complete light blocking part 17 b is formed as a light blockingpattern of the entire standard-pattern mask part M2 and an adjacentregion to the boundary line LB2.

Meanwhile, the HT mask part 17 a is formed as a region where the entirelight blocking pattern 41 except the portion of the complete lightblocking part 17 b is formed.

In the third mode, the second exposure process is performed with thetriton mask 16 shown in FIG. 22, in the same fashion as the first mode.

The result is that the region EX3 shown in FIG. 23 is subjected to thefirst exposure process with the complete light blocking part 17 b, andthe second exposure process with the complete light blocking part 16 b.Accordingly, like the region EX2, no part of the region EX3 is subjectedto light transmission during the first exposure process. It is desiredthat the shift amount ΔD3 should be set a little wider than (the shiftamount ΔD2+the predetermined amount C) in order to prevent two lighttransmissions through the region EX3 with reliability.

(Forming Accuracy of Connection Region)

FIGS. 26 to 28 illustrate optical simulation results of connectionregions (which correspond to the region EX3 shown in FIG. 23) of therespective resist patterns obtained by the pattern forming methods inthe first to third modes according to the third preferred embodiment.

As shown, in a simulation result of FIG. 26 (first mode), a connectionportion 76 corresponding to the wiring pattern extension parts 23 c and24 c does not taper off in wiring width, but has a stable shape toalmost the same degree as the forming width of the line patterns in agrating-pattern forming region All. However, in simulation results ofFIGS. 27 and 28 (second and third modes), connection portions 77 and 78corresponding to the wiring pattern extension parts 23 c and 24 c taperoff, and have unstable shapes.

It is confirmed from the above simulation results that, as for theconnection region (which corresponds to the region EX3 shown in FIG. 23)between the grating pattern 100 and standard pattern 101, the first modeis most suitable where an HT mask part is used both in the first andsecond exposure processes, namely, where an HT mask part is used in anadjacent region to the boundary line LB2 both in the first and secondexposure processes. This is due to the fact that optical image contrastis enhanced for fine patterns in the connection region by using an HTmask both in the first and second exposure processes.

As for the regions EX1 and EX2 that are subjected to substantially thesame first and second exposure processes in the first to third modes,there is no difference between these two regions. Although the completelight blocking parts are effective when having a smaller transmissionfactor than the light blocking part having a transmission factor ofabout 6%, it is desired that the complete light blocking parts shouldblock light completely (transmission factor of 0%).

(Fourth Mode)

FIG. 29 illustrates a triton mask used in the first exposure process ina fourth mode according to the third preferred embodiment. As shown, atriton mask 19 for the first exposure process includes an HT mask part19 a, which is an incomplete light blocking part, and a complete lightblocking part 19 b. The relationship between the parts 19 a and 19 b isthe same as that between the HT mask part 15 a and complete lightblocking part 15 b of the triton mask 15 used in the first mode.

The triton mask 19 differs from the triton mask 15 in that the lightblocking pattern 41 on the HT mask part 19 a is increased in thicknessby about 6 nm in total on its both sides to about 71 nm in an adjacentregion to the boundary line LB3. That is, the triton mask 19 differsfrom the triton mask 15 in additionally providing light blocking patternextension parts 41 d each of which extends from one side of the lightblocking pattern 41 toward the transmissive pattern 42 by about 3 nm.The remaining structure is the same as the triton mask 15, so thedescription thereof is omitted.

In the fourth mode, the second exposure process is performed with thetriton mask 16 shown in FIG. 22, in the same fashion as the first mode.

In this manner, in the pattern forming method of the fourth modeaccording to the third preferred embodiment, the first and secondexposure processes are performed with the triton masks 19 and 16,respectively. Therefore, the same effects as the first mode areobtained.

Further in the fourth mode, connection to the standard pattern 101 canbe established with stability by partially increasing the forming widthof the light blocking pattern 41 near the connection region to thestandard pattern 101.

Therefore, in the third preferred embodiment, an exposure mask setincluding the HT masks 15, 17 and 19 for the first exposure and HT masks16 and 18 for the second exposure is used so that a pattern including agrating pattern and standard pattern can be formed on the resist withhigh accuracy.

Application to First Embodiment

The first to fourth modes described above may be applied to the firstpreferred embodiment. In such cases, no part of the region EX1equivalent to the most part of the line patterns 11 to 14 is subjectedto light transmission during the second exposure process. This preventsthe line patterns 11 to 14 in the region EX1 from being subjected tohalf-tone transmitted light, and allows the line patterns 11 to 14 to beobtained with high accuracy.

In addition, no part of the region EX2 equivalent to the most part ofthe patterns 21 to 24 is subjected to light transmission during thefirst exposure process. This prevents the patterns 21 to 24 in theregion EX2 from being subjected to half-tone transmitted light, andallows the patterns 21 to 24 to be obtained with high accuracy.

In the first preferred embodiment, the first mode where an HT mask partis used for the connection region (which corresponds to the connectionregion A3 shown in FIG. 2) both in the first and second exposureprocesses should be applied again to increase the possibility ofenhancing optical image contrast, as in the second preferred embodiment.

Fourth Preferred Embodiment

FIG. 30 illustrates a flow chart for an exposure method to be performedon a plurality of wafers according to a fourth preferred embodiment ofthis invention. A general process is performed in the same fashion asthe first preferred embodiment illustrated in FIG. 1, except that thismethod is performed on a plurality of wafers (predetermined substrate ofeach wafer) and that the steps S3 and S4 are performed as shown in FIG.30.

For convenience of explanation, the first exposure process with the HTmask 1 and the second exposure process with the HT mask 4 will bedescribed as an example in the fourth preferred embodiment.

Turning to FIG. 30, at step S11, the first exposure process with the HTmask 1 is performed on (a predetermined substrate of) a first wafer tobe exposed. Then, at step S12, the HT mask 1 is exchanged for the HTmask 4, and the second exposure process with the HT mask 4 is performedon the first wafer to be exposed.

Processing then continues with step S13 where the presence or absence ofunexposed wafers is checked, and then moves on to step S14 when theyexist (YES), or is completed when they do not (NO).

At step S14, the first wafer is replaced by a new wafer to be exposed.That is, one of the unexposed wafers is mounted on an exposure device asa second wafer to be exposed.

Then, at step S15, the second exposure process is performed on (apredetermined substrate of) the second wafer to be exposed bysuccessively using the HT mask 4 that was used in step S12 and has notbeen exchanged. Then, at step S16, the HT mask 4 is exchanged for the HTmask 1, and the first exposure process with the HT mask 1 is performedon the second wafer to be exposed.

Processing then continues with step S17 where the presence or absence ofunexposed wafers is checked, and then moves on to step S18 when theyexist (YES), or is completed when they do not (NO).

At step S18, the second wafer is replaced by a new wafer to be exposed.That is, one of the unexposed wafers is mounted on the exposure deviceas a third wafer to be exposed.

Processing then returns to step S11 where the first exposure process isperformed on (a predetermined substrate of) the third wafer to beexposed by successively using the HT mask 1 that was used in step S16and has not been exchanged. Then, at step S12, the HT mask 1 isexchanged for the HT mask 4, and the second exposure process with the HTmask 4 is performed on the third wafer to be exposed.

Steps S11 to S18 are repeated thereafter until the absence of unexposedwafers has been confirmed at step S13 or step S17.

In this manner, in the exposure method according to the fourth preferredembodiment, either one of the first and second exposure processes isperformed successively on two successively exposed wafers. This requiresonly one exchange of masks for two-exposure processes (first and secondexposure processes), resulting in a reduction in processing timerequired for mask exchange, which further results in a reduction inoverall processing time of the pattern forming method for a plurality ofwafers.

Each of the first and second exposure processes may in some instancesinclude a plurality of exposure steps by a plurality of masks. When thesecond exposure process is done by first to third partial exposure steps(not in particular order), for example, step S12 should be performed byfirst, second and third partial exposure steps in this order, and stepS15 should be performed by third, second and first partial exposuresteps in this order. This results in a reduction in processing timerequired for mask exchanges between the partial exposure steps by thetime required for a mask exchange at the third partial exposure step.

<Application to Semiconductor Device Manufacturing Method>

The pattern forming methods (including the case where the exposuremethod according to the fourth preferred embodiment is incorporated)described in the first to third preferred embodiments may be applied tosemiconductor device manufacturing methods.

That is, semiconductor device manufacturing methods to which the patternforming methods according to this invention are applied would include afirst step of applying a resist to a semiconductor substrate surface oran object to be patterned inside the semiconductor substrate, a secondstep of subjecting the resist to patterning with one of the patternforming methods according to the first to third preferred embodiments,and a third step of subjecting the object to be patterned to patterningwith the patterned resist as a mask.

The result is that a pattern including a grating pattern and a standardpattern that are formed continuously with each other through aconnection pattern can be formed on the object to be patterned with highaccuracy.

<Others>

In the first to third preferred embodiments, the resist subject to thefirst and second exposure processes is made of a positive type resistmaterial to obtain the convex grating pattern and standard pattern.

Alternatively, a chemically amplified negative type resist may be usedto obtain the same effects as the first to third preferred embodimentsin forming a trench-type wiring pattern.

FIG. 31 illustrates the structure of another illumination system stopused in the second exposure process. As shown, an illumination systemstop 48 includes four circular openings 49. The use of this illuminationsystem stop 48 allows for four-lens illumination.

In this manner, four-lens illumination may be used instead of the ⅔annular illumination (see FIG. 6) as illumination for the secondexposure process described in the first to fourth preferred embodiments.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

1. A pattern forming method on a resist formed on a predeterminedsubstrate, said resist including adjacent first and second regions to bepatterned, said method comprising the steps of: (a) performing a firstexposure process with a first exposure mask using dipole illuminationsubstantially on said first region of said resist, said first exposuremask having a repetition pattern in which a line and space are repeatedalternately; (b) performing a second exposure process with a secondexposure mask substantially on said second region of said resist, saidsecond exposure mask having a standard pattern that is a patternexcluding said repetition pattern, said standard pattern at leastpartially including a connection pattern continuous with said repetitionpattern; and (c) performing a development process on said resist havingbeing subjected to said steps (a) and (b).
 2. The pattern forming methodaccording to claim 1, wherein said first and second exposure masks eachinclude first and second mask parts corresponding to said first andsecond regions of said resist, respectively, said first exposure mask isprovided with a pattern for forming said repetition pattern on saidfirst mask part, and a light blocking region on the whole surface ofsaid second mask part, and said second exposure mask is provided with apattern for forming said standard pattern on said second mask part, anda light blocking region on the whole surface of said first mask part. 3.The pattern forming method according to claim 1, wherein said first andsecond exposure masks each include first and second mask partscorresponding to said first and second regions of said resist,respectively, said first exposure mask is provided with a pattern forforming said repetition pattern on said first mask part, and a lightblocking region on the whole surface of said second mask part, and saidsecond exposure mask is provided with a pattern for forming saidstandard pattern on said second mask part, and an extension part of saidconnection pattern of said standard pattern and a light blocking regionon said first mask part, said extension part being provided in a firstextension region extending inwardly from a boundary line between saidfirst and second mask parts by a first predetermined amount, said lightblocking region being provided on the whole surface of a regionexcluding said first extension region and a second extension region,said second extension region extending inwardly from an edge linecorresponding to an edge position of said pattern for forming saidrepetition pattern by a second predetermined amount.
 4. The patternforming method according to claim 3, wherein a direction in which saidline in said repetition pattern is formed is defined as a firstdirection, and a direction orthogonal to said first direction is definedas a second direction, and said first and second predetermined amountsinclude an amount in view of the amount of edge recession of a patternfor forming said space in said repetition pattern, and the amount ofoverlay deviation in said first direction between said first and secondexposure masks of said steps (a) and (b).
 5. The pattern forming methodaccording to claim 4, wherein a forming width of said extension part ofsaid connection pattern is equivalent to the sum of a forming width of apattern for forming said line in said repetition pattern and an amountin view of the amount of overlay deviation in said second directionbetween said first and second exposure masks of said steps (a) and (b)and the amount of dimensional accuracy tolerance.
 6. The pattern formingmethod according to claim 3, wherein said first and second exposuremasks each include a transmissive part, a half-tone phase shift maskpart transmitting light only at a predetermined ratio and inverting aphase of light being transmitted therethrough, and a light blocking parthaving a smaller transmission factor than said predetermined ratio, saidsecond mask part of said first exposure mask is formed at least of saidlight blocking part in a region excluding a boundary adjacent regionbetween said first and second mask parts, said first mask part of saidsecond exposure mask is formed at least of said light blocking part in aregion excluding said boundary adjacent region.
 7. The pattern formingmethod according to claim 6, wherein both of said first and secondexposure masks are formed of said half-tone phase shift mask part insaid boundary adjacent region.
 8. The pattern forming method accordingto claim 7, wherein said first exposure mask is locally widened informing width in a region adjacent to said second mask part, withrespect to a pattern corresponding to said line in said first mask part.9. The pattern forming method according to claim 1, wherein saidpredetermined substrate including a plurality of substrates classifiableby the wafer, and said steps (a) and (b) are performed on said pluralityof substrates in a changed sequence.
 10. The pattern forming methodaccording to claim 1, wherein said resist includes a positive typeresist.
 11. The pattern forming method according to claim 1, whereinsaid repetition pattern includes a first partial repetition pattern inwhich a line and space are repeated in a first direction and a secondpartial repetition pattern in which a line and space are repeated in asecond direction orthogonal to said first direction, and said firstexposure mask includes first and second partial repetition pattern maskshaving said first and second partial repetition patterns, said step (a)comprising the steps of: (a-1) performing an exposure process with saidfirst partial repetition pattern mask on said resist, under a firstillumination condition using dipole illumination in which twin lensesare arranged in said first repetition direction; and (a-2) performing anexposure process with said second partial repetition pattern mask onsaid resist, under a second illumination condition using dipoleillumination in which twin lenses are arranged in said second repetitiondirection.
 12. A semiconductor device manufacturing method, comprisingthe steps of: (a) forming a resist on a semiconductor substrate or anobject to be patterned inside said semiconductor substrate; (b)patterning said resist using the pattern forming method recited in claim1; and (c) patterning said object to be patterned with said resisthaving been patterned as a mask.
 13. An exposure mask set comprising: afirst exposure mask including adjacent first and second mask parts, saidfirst mask part having a repetition pattern in which a line and spaceare repeated alternately; and a second exposure mask including first andsecond mask parts equivalent to said first and second mask parts of saidfirst exposure mask, said second mask part having a standard patternthat is a pattern excluding said repetition pattern, at least part ofsaid standard pattern including a connection pattern for beingcontinuous with said repetition pattern, wherein said first exposuremask is provided with a light blocking region on the whole surface ofsaid second mask part, said second exposure mask is provided with alight blocking region on at least part of said first mask part, saidfirst and second exposure masks each include a transmissive part, ahalf-tone phase shift mask part transmitting light only at apredetermined ratio and inverting a phase of light being transmittedtherethrough, and a light blocking part having a smaller transmissionfactor than said predetermined ratio, said second mask part of saidfirst exposure mask is formed at least of said light blocking part in aregion excluding a boundary adjacent region between said first andsecond mask parts, said first mask part of said second exposure mask isformed at least of said light blocking part in a region excluding saidboundary adjacent region.
 14. The exposure mask set according to claim13, wherein both of said first and second exposure masks are formed ofsaid half-tone phase shift mask part in said boundary adjacent region.15. The exposure mask set according to claim 13, wherein a direction inwhich said line in said repetition pattern is formed is defined as afirst direction, and a direction orthogonal to said first direction isdefined as a second direction, said second exposure mask is providedwith an extension part of said connection pattern of said standardpattern and a light blocking region on said first mask part, saidextension part being provided in a first extension region extendinginwardly from a boundary line between said first and second mask partsby a first predetermined amount, said light blocking region beingprovided on the whole surface of a region excluding said first extensionregion and a second extension region, said second extension regionextending inwardly from an edge line corresponding to an edge positionof said pattern for forming said repetition pattern by a secondpredetermined amount, said first and second predetermined amountsinclude an amount in view of the amount of edge recession of a patternfor forming said space in said repetition pattern, and the amount ofoverlay deviation in said first direction at the time of exposure usingsaid first and second exposure masks, and a forming width of saidextension part of said connection pattern is equivalent to the sum of aforming width of a pattern for forming said line in said repetitionpattern and an amount in view of the amount of overlay deviation in saidsecond direction at the time of exposure using said first and secondexposure masks and the amount of dimensional accuracy tolerance.